what you are looking for in addition to the nudi is a cluch of eggs.these eggs look like an @ symbol.they are simple to spot but a pain in the butt.get yourself a small tub or container,12" tweezers,a magnifying glass,gloves,and some lugols solution.
with these items in hand take the zoas or monties out one at a time and inspect them for eggs or nudi's. when you find the infected coral,check other same corals. make up a dip bath as per the directions on the lugols bottle (use water from the tank) then dip the coral in and swish it to and fro this will get rid of the nudis but not the eggs.with the eggs you have to pick them off carefully as not to break the thread.after the dip place corals back in a location where you can easily watch them in case you missed any culprits. this will rid you of the one that are on the corals keep an eye out for wanderers on glass or rock. by the way the dip will help the corals heal and open up faster. good luck.
BY THE WAY DON'T FORGET THE GLOVES,EXTREMELY IMPORTANT.